This invention relates to an apparatus for detecting a blockage in flow of particles through a duct, which is particularly but not exclusively designed and arranged for use with seeders or planters where the particles passing through the duct are seeds.
The apparatus can be used for both air seeders where the seeds are carried through the duct in an air stream or can also be used with planters or seed drills where the seeds are dropped by gravity through a feed tube. The term xe2x80x9cparticlesxe2x80x9d used herein is not intended to indicate any size of the elements passing through the duct.
There have previously been proposed systems for counting the number of seeds flowing in a duct and generally such systems utilize optical sensors at the duct including a transmitter on one side of the duct and a receiver on the other side of the duct arranged so that substantially the whole of the duct is visible in the light zone between the two elements.
Various designs have been proposed in a number of prior art patents including for example U.S. Pat. No. 5,883,383 (Dragne) assigned to the present assignees. These devices are relatively complex and therefore carry a significant cost. The devices are primarily designed for counting seeds in a seed duct and some operators choose to avoid the complexity and cost of an accurate counting system and require only a system which indicates blockage of a tube.
Air seeders are particularly prone to blockages at the seed discharge duct and unless the blockage is detected, the seeder can continue operating for a considerable period of time while missing a whole row thus leading to a significant loss in production in the finished crop.
One example of a blockage monitor of this type is shown in U.S. Pat. No. 5,177,470 (Repas) assigned to the present assignees. This arrangement includes a pin sensor which projects through the wall of the duct into the interior of the duct so that some of the seeds passing through the duct impinge upon the pin causing generation of a pulse by a piezo-electrical crystal in the pin. This device has achieved significant commercial success but some concern has arisen due to the use of a projecting element which extends into the duct and therefore can itself interfere with the flow of seeds.
There is therefore a desire to replace the projecting pin with an alternative system for detecting the passage of seeds which avoids elements projecting into the interior of the duct.
U.S. Pat. No. 5,831,542 (Thomas et al ) assigned to Deere and company discloses a flexible generally flat piezo electric seed sensor element inserted at an acute angle of about thirty degrees into the seed flow duct. This is intended to replace the projecting pin and thus reduce the impingement of the detection system into the duct itself. However, there is still some interference with the flow of seeds by the detection system so that this proposal does not wholly overcome the problem.
A further alternative arrangement utilises the same transmitter and receiver in the seeder system which is proposed for seed counting systems. This arrangement can operate effectively, as has been evidenced by the success of the seed counting system, but carries a significant additional cost in due of the complexity of the sensor element and the greater difficulty of communication with that sensor element. Such sensor elements generally require the use of a three wire transmission system to separate the power supply from the signal transmission to allow detection of the signal at the separate blockage module.
Further elements relevant to the above U. S. Pat. No. 5,831,542 are shown in U. S. Pat. Nos. 5,923,262, 5,831,541 and 5,831,539, all assigned to Deere and company.
It is one object of the present invention to provide an improved blockage monitor which allows a simple inexpensive construction without any impingement of the sensor into the duct.
According to a first aspect of the invention there is provided an apparatus for detecting a blockage in flow of particles through a duct comprising:
a sensor having a sensor body for mounting on a wall of the duct and a sensor face for presentation to the interior of the duct;
a light source mounted on the sensor body for projecting light from the light source through the sensor face into the interior of the duct;
a light receptor mounted on the sensor body at the sensor face adjacent the light source so as to be responsive to light projected into the interior of the duct and reflected from surfaces in the duct to produce an output signal proportional to the intensity of reflected light received such that the output signal varies as a particle passes the sensor face;
a monitoring circuit responsive to the output signal to generate therefrom an output including a series of pulses representative of the passage of any particles;
a blockage module for receiving the output and for determining from the output whether there is a blockage of the duct sufficient to interfere with the flow of particles and to generate a warning signal in the event that a blockage is detected.
Preferably the sensor body includes a raised portion defining the sensor face which is substantially flush with an inside surface of the duct such that the light source and the receptor do not interfere with flow of particles.
Preferably the monitoring circuit is in the sensor body, wherein the blockage module is spaced from the sensor body and wherein a power voltage is supplied to the sensor using two wires only and the output including the series of pulses is communicated along the same two wires.
Preferably the monitoring circuit includes a comparator circuit for detecting when a change in the output signal exceeds a predetermined threshold and a communication circuit operable by the comparator circuit to generate a current pulse transmitted along the two wires detectable by the blockage module.
Preferably the communication circuit includes a transistor switch operable for connecting a current across the two wires to generate a current pulse which can be detected at the blockage module.
Preferably the light source includes a time delay circuit by which the LED current is delayed relative to a variation of power voltage on the connecting wires.
Preferably the light source includes a power supply which receives a power voltage from the blockage module along the connecting wires, wherein the blockage module is arranged to effect a test of the sensor by communicating to the sensor a pulse in the power voltage so as to generate a corresponding but delayed pulse in the light from the light source and wherein the monitoring circuit produces a pulse so that it is detectable by the blockage module separately from the pulse in the power voltage.
Preferably the blockage module including a processor providing a counter for counting the number of pulses in a predetermined time period and providing an algorithm for determining from the counted number whether there is a blockage; wherein there is provided a ground speed indicator for providing a speed input indicative of a ground speed of movement of the duct across ground onto which the particles are to be applied; and wherein there is provided a communication system for communicating the speed input to the blockage module for modifying the algorithm in dependence upon the ground speed.
Preferably the processor is arranged such that the algorithm includes a comparison of the counted number with a calibration counted number determined during a calibration period at a first ground speed, wherein there is determined to be a blockage when the counted number is reduced relative to the calibration number by a predetermined ratio and wherein the ratio is changed in dependence upon a difference between the ground speed and the calibration ground speed.
Preferably there is provided a plurality of ducts and a plurality of respective sensors and wherein each sensor has associated with it its own calibration counted number.
Preferably there is provided an application rate indicator for providing an application rate indicative of an intended rate of application of the particles to the ground onto which the particles are to be applied and the communication system is arranged for communicating the application rate to the blockage module for modifying the algorithm in dependence upon a change in intended application rate.
According to a second aspect of the invention there is provided an apparatus for detecting a blockage in flow of particles through a duct comprising:
a sensor for mounting on a wall of the duct;
the sensor having a light source for projecting light from the light source into the interior of the duct;
the sensor having a light receptor arranged to produce an output signal proportional to the intensity of light received such that the output signal varies as a particle passes the sensor;
the sensor having a monitoring circuit responsive to the output signal to generate therefrom an output including a series of pulses representative of the passage of any particles;
a blockage module for receiving the output and for determining from the output whether there is a blockage of the duct sufficient to interfere with the flow of particles and to generate a warning signal in the event that a blockage is detected;
wherein the blockage module is spaced from the sensor and wherein a power voltage is supplied to the sensor using two wires only and the output including the series of pulses is communicated along the same two wires;
wherein the monitoring circuit includes a comparator circuit for detecting when a change in the output signal exceeds a predetermined threshold and a communication circuit operable by the comparator circuit to generate a current pulse transmitted along the two wires detectable by the blockage module;
wherein the light source includes a power supply which receives a power voltage from the blockage module along the connecting wires;
wherein the blockage module is arranged to effect a test of the sensor by communicating to the sensor a pulse in the power voltage;
wherein the sensor is arranged so as to generate a corresponding but delayed pulse in the light from the light source;
and wherein the monitoring circuit generates the current pulse from the delayed pulse in light such that the delayed current pulse is detectable by the blockage module separately from the pulse in the power voltage.
According to a third aspect of the invention there is provided an apparatus for detecting a blockage in flow of particles through a duct comprising:
a sensor for mounting on a wall of the duct;
the sensor having a receptor arranged to produce an output including a series of pulses representative of the passage of any particles;
a blockage module for receiving the output and for determining from the output whether there is a blockage of the duct sufficient to interfere with the flow of particles and to generate a warning signal in the event that a blockage is detected, the blockage module including a processor providing a counter for counting the number of pulses in a predetermined time period and providing an algorithm for determining from the counted number whether there is a blockage;
a ground speed indicator for providing a speed input indicative of a ground speed of movement of the duct across ground onto which the particles are to be applied;
and a communication system for communicating the speed input to the blockage module for modifying the algorithm in dependence upon the ground speed.
Preferably the processor is arranged such that the algorithm includes a comparison of the counted number with a calibration counted number determined during a calibration period at a first ground speed, there is determined to be a blockage when the counted number is reduced relative to the calibration number by a predetermined ratio and the ratio is changed in dependence upon a difference between the ground speed and the calibration ground speed.
Preferably there is provided a plurality of ducts and a plurality of respective sensors and wherein each sensor has associated with it its own calibration counted number.
Preferably there is provided an application rate indicator for providing an application rate indicative of an intended rate of application of the particles to the ground onto which the particles are to be applied and the communication system is arranged for communicating the application rate to the blockage module for modifying the algorithm in dependence upon a change in intended application rate.